The problem confronting the fresh fish industry is enormous. In its February, 1992 issue, Consumer Reports published the results of a six month investigation regarding fresh fish. In the industry, fresh fish refers to fish that has not been frozen. The extensive report raises questions concerning the quality and wholesomeness of fresh fish and the safety of consumers eating the fish.
The information contained in this Consumers Report article entitled "Is Our Fish Fit to Eat?" is hereby incorporated herein by reference in its entirety.
Information concerning trimethylamine and trimethylamine oxide is extensive and well known. The Journal of the Fisheries Research Board of Canada, volume 6, published in 1945 includes articles entitled "Factors Affecting Triamineoxidease" by J. B. Neilands; "Amines in Fish Muscle: I. Colormetric Determination of Trimethylamine as the Picrate Salt" by W. J. Dyer; and "Amines in Fish Muscle: II. Development of Trimethylamine and Other Amines" by W. J. Dyer and Yvonne A. Mounsey. These 1945 articles are hereby incorporated herein by reference in their entireties.
U.S. Pat. No. 4,832,972 discloses a supercooling process for tropical fish that produces a high salt content in the supercooled fish maintained in a non-frozen state at temperatures in the range of about 0.degree. to about -5.degree. C. The fresh fish treatments include thermal blanching treatments at about 90.degree. C. and treating the fish with an antimicrobial agent.
Marine organisms have body fluids of slightly higher tonicity than seawater to prevent the loss of body water by osmosis to the surrounding seawater. Trimethylamine N-oxide (TMAO) is an odorless metabolite commonly found in marine fish and contributes to intracellular osmolarity. The tissues of marine fish contain high concentrations of TMAO that enable the fish to live in salty water. The TMAO counteracts the tendency of seawater to extract water from the fish tissues.
During the spoilage of fish, bacteria in fish flesh reduce TMAO in the fish tissues to trimethylamine (TMA), which primarily supplies the characteristic odor and flavor of spoiled marine fish. That is, TMA is the normal bacterial breakdown product of TMAO.
Bacteria from the skin and intestines of fish reduce TMAO in the absence of oxygen, scarcity of oxygen, or under low oxygen conditions. In other words, the bacteria use TMAO for life in the absence of oxygen. TMA concentrations in fish muscle may be used as the indicator of the extent and rate of fish spoilage. Levels above 15 mg TMA-N (1.08 mmoles TMA)/100 grams of fish flesh are considered in the industry to be a sign of spoilage in fish.
Typically, any bacteria live only over a temperature span of about 30-40.degree. C. The temperature span for a specific organism is determined primarily by the lipid composition of its cellular membranes. The cellular membrane rigorously controls the entry and exit of materials forming a living cell. Therefore, the cellular membrane is a key to life. It protects the intracellular environment from dangerous components of the external environment, and maintains an environment for the stability and functioning of cellular components and reactions.
At temperatures above the upper temperature limit for life, the lipids in the cellular membrane melt and thereby destroy the barrier formed by the cellular membrane. Cold water fish inhabiting waters of 0-10.degree. C. have bacteria associated with them that are adapted to those environmental temperatures.
The alginate coating process used in the present invention is disclosed in U.S. Pat. Nos. 3,255,021; 3,395,024; and 3,991,218. These earlier patents disclose the use of an alginate-containing solution and a gelling solution used in sequence to form a substantially continuous film over a substrate such as meat, seafood, poultry and the like.
The coating solution is composed of sodium alginate and maltodextrin dissolved in water. The substrate is first dipped into the coating solution and then dipped into a gelling solution of calcium chloride thickened by a trace amount of cellulose gu dissolved in water.
The disclosures of U.S. Pat. Nos. 3,255,021; 3,395,024; and 3,991,218 are hereby incorporated herein by reference in their entireties. Thus, a further detailed disclosure of the particular manner of forming the edible continuous alginate coating is unnecessary. However, it has been found that the particular temperatures and pH values for the separate coating solutions as disclosed herein produce unexpected results.
Moreover, through experimentation, we discovered that lactic acid used in combination with the gelling solution does not reduce spoilage-causing bacteria, which cause the reduction of TMAO to TMA.